[Sender]

It's not just learning a sufficient vocabulary, a different grammar and reading swirly doodles backwards. And beyond that, it's not just learning to speak without an accent, which as you pointed out is very unlikely.

What really takes time and immersion is learning the hidden and implied meaning of phrases and words placed together. A translator could get every word correct and yet miss an important statement due to lack of knowledge of the culture and colloquialisms.

For example, if you trained a non-English speaker to translate English word for word in 6 months, and he/she translated phrases correctly such as "on the ball" or "under the table" or "light in the loafers", they may miss the whole meaning of the paragraph and toss it as irrelevant nonsense. I'm sure there are many such hidden meanings in Arabic text that go in one shredder and out the other.

[Diogenesis]

One good example is: "I will chop down the tree, and then chop up the tree."

[angkor]

miss an important statement due to lack of knowledge of the culture and colloquialisms.

If one is taught from a dictionary that might be true. But that's not the way most training is done.

If a translator saw a phrase like "light in the loafers", it would make no logical sense in context and if translated literally. So one is more likely to ask a colleague "what does this mean, it makes no sense."

If a person is trained and understands 95 percent of the language, then oddities and colloquialisms are going to stand out and require further analysis. Even native speakers encounter this in their own language (e.g. "metrosexual" or any known hip-hop lyrics).